You are missing a Java library called oxygen-jfx-components.jar. I think you could pick it up from a standalone Oxygen XML Editor installation (from the "lib" folder). I will also discuss with my colleague who knows more about how the SDK was mavenized, see if we exposed this library via Maven or not.

Do you happen to have a retina/ HiDpi screen?I will send you an email with a modified version of oxygen-jfx-components.jar that contains a possible fix to this issue. You can replace the exisitng one inside {oxygenInstallDir}/lib and test again.

We tested on multiple stations and operating systems but we didn't reproduce this behavior. You are also the only one that reported this situation so far. Can you test an Oxygen version 19 and see if the same behavior happens when opening samples\form -controls\about\form-controls.xml? Perhaps we've solved it without even knowing...

Do you have a custom DPI (Dots per Inch) size setting? Perhaps it will also help if you send us more information about your system. The fastest way to do that is to go inside Oxygen to Help->Report problem... and just send us the report.